1. Field of the Invention
This invention relates to water or liquid sealing traps such as used to connect the waste water outlet of a wash-basin, sink or the like to a waste water drainage system.
2. Description of the Prior Art
It is generally known that a permanent water seal is required in the water trap to assure the normal function of a waste water outlet installation and to prevent contaminated air from the sewer from contacting the surrounding atmosphere.
A water trap of this kind may be U shaped with one leg connected to a sanitary appliance, such as a wash basin or the like, and the other leg connected to the waste water system. Another embodiment of the water trap may be in the shape of a bottle-like container, in the centre of which extends a vertical pipe connected to the water basin and having an outlet for connection with the waste water pipe.
Existing water traps of the two kinds have been provided with an air admittance valve in order to eliminate negative air pressure which may occur in the drainage system, especially when flushing down an amount of waste water through the vertical parts of the waste water pipes. In such cases air suction may be such that the water contained in the water traps is sucked away, breaking the water seal.
A U-shaped water trap provided with an air admittance valve has already been disclosed in U.S. Pat. No. 605,202 which is related to a trap for sinks, the outlet pipe of which being provided with a valve that seats itself by gravity. This air admittance valve is extending upwards from the outlet pipe which diminishes the available space around the water trap and which is positioned in such a way that it may be accidentally tampered and damaged preventing the normal working of the valve.
The patent documents GB 856.064 and GB 1.220.982 also refer to water or liquid sealing traps provided with air admittance valves. In the first document the valve is either applied to the outlet leg of a U-shaped version of the trap and the inlet leg is connected to a wash basin or the like or to the cylindrical head of the container in a bottle shaped version. In this case the non return air valve is fitted on the side opposite the outlet pipe to the sewer. In both cases the position of the valve is an obstacle to easy fitting of the water trap in a generally confined spaced.
Document GB 1.397.705 discloses a bottle shaped trap with a non return valve provided inside the water trap body and more precisely in a separation wall between the inlet area and the outlet pipe above the static liquid level. The port by-passing the liquid seal and the valve includes means whereby it is normally held closed but opens upon suction in the outlet pipe to admit air from the inlet area to break the suction. In this case the valve is not protruding the outer configuration of the water trap but is situated in an area where it is constantly subject to (waste) humid atmosphere and sediment of waste water passing through the water trap, causing clogging of the valve membrane.
Finally, document GB 2 005 749 discloses a water trap of the bottle shaped version including an annular air admittance valve situated in the upper portion of the container. In this case the valve is completely separate from the waste water flow, but the overall dimensions of the container and valve is rather important, especially in confined spaces.